Fluid sensing and amplifying nozzle and control

ABSTRACT

A fluid sensing and amplifying system comprising a sensing head having a pair of pilot fluid discharge nozzles coacting to sense edge position and directed toward respective interior chambers, flexible diaphragms having one side thereof exposed to pressure in the respective chambers and having plates carried at the opposite side thereof controlling respective working fluid discharge orifices, the pressure variations upstream of said working orifices being of magnitude to directly control an edge position correcting device for a moving web, the device automatically shifting to a quiescent condition in response to a failure of fluid pressure to the sensing head.

United States Patent [72] lnventors Paul W. .lacobsen; [56] References Cited Richard N. Klaeser, Kiel, Wis. UNITED STATES PATENTS flig- 1332 2,884,495 4/1959 Frankel 73/37.7UX

9 Patented Jan. 5,197] 3,260,434 7/1966 Jacobsen 226/22X [73] As ignee H. G. Weber and Com any, In Primary ExaminerRichard A. Schacher Kiel, Wis. Attorney-Hill, Sherman, Meroni, Gross & Simpson a corporation of Wisconsin ABSTRACT: A fluid sensing and amplifying system comprising a sensing head having a pair of pilot fluid discharge nozzles coacting to sense edge position and directed toward respective interior chambers, flexible diaphragms having one side thereof [54] g gg gg AND AMPLIFYING NOZZLE AND exposed to pressure in the respective chambers and having 15 Cl 4 D plates carried at the opposite side thereof controlling respecrawmg tive working fluid discharge orifices, the pressure variations [52] US. Cl 226/22, upstream of said working orifices being of magnitude to 73/37]: 226/46 directly control an edge positioncorrecting device for a mov- [5l] Int. Cl B65h 25/26 ing web, the device automatically shifting to a quiescent con- [50] Field of Search 226/22, 46; dition in response to a failure of fluid pressure to the sensing 73/37.7 head. r

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PATENTEU JAN 5197:

SHEET 2 OF 2 INVENTORS 1% s Maw/$52 2 ZZZ/[W W m/ i,

FLUID SENSING AND AMPLIFYING. NOZZLE AND CONTROL SUMMARY OF THE INVENTION This invention relates to a fluid pressure operated sensing and amplifying head and to a system incorporating such a head for controlling the position of an edge of a moving web.

It is a particular object of the present invention to provide a compact fluid pressure operated sensing head supplying a greatly amplified error signal and which utilizes an interior diaphragm as the only moving part.

It is a further object of the present invention to provide such a fluid pressure operated sensing head which is of extremely simple and economical construction and which is highly reliable in operation.

A further more specific object of the present invention is to provide a fluid pressure operated sensing and amplifying system which is particularly adapted for use in conjunction with a conventional edge position correcting device and which is capable of developing a working error signal for directly controlling such conventional device.

Yet another object of the present invention resides in a sensing system for applying successive corrections to a web in response to an existing error but wherein a failure of the fluid pressure supply to the sensing head will result in overriding of the error response of the correction device to place the device in a quiescent condition.

Other objects, features and advantages of the present invention will be apparent from the following detailed description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1.is a somewhat diagrammatic plan view of a sensing head in accordance with the present invention;

FIG. 2 is a vertical sectional view taken generally along the line 11-11 ofFIG. 1;

FIG. 3 is a diagrammatic illustration of an overall system in accordance with the present invention, including a partial showing of the sensing head and a showing of the edge position correcting device being held in the quiescent condition in response to a failure of fluid pressure to the sensing head; and

FIG. 4 is a partial view of the edge correcting device of FIG. 3 but showing the device conditioned by an error signal from the sensing head for producing successive edge correction movements.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, there is illustrated a preferred form of fluid pressure operated sensing and amplifying head in accordance with the present invention. The sensing head 10 includes an upstanding mounting pin 11 having a reduced diameter portion 11a. As indicated in dotted outline, the sensing head may be mounted to a suitable web apparatus by means of a mounting arm 12 secured to the apparatus and having an aperture 12a receiving the pin 11. A setscrew is indicated at 13 which cooperateswith the reduced diameter portion 11a for maintaining the vertical and rotary position of the sensing head 10.

The web apparatus which is not shown in detail may comprise any conventional paper machine or the like wherein a web 15 such as a felt or wire has a longitudinal edge 150 whose lateral position is to be controlled as the web moves longitudinally, for example in the direction of arrow 16, FIG. 1.

Referring to the orientation shown in FIG. 2, the sensing head includes a lower member 18 having a fluid input passage 19 which is connected by a line diagrammatically indicated at 20, FIG. 3, to a supply of pilot fluid pressure. The conduit 19 connects with respective pilot fluid discharge nozzles 22 and 23 which are preferably formed in respective frustoconical bosses 24 and 25. The discharge nozzles 22 and 23 direct respective pilot fluid jets toward respective receiving apertures indicated at 28 and 29 in an upper sensing head member 30. Wall means of the sensing head member 30 defines an exterior surface 32 toward which the pilot jets are directed and provides internal diaphragm chambers 35 and 36 in association with a diaphragm material generally indicated at 38.

Referring to the portion of the diaphragm 38 associated with chamber 36, it will be observed that the diaphragm part 40 which is free to move in response to pressure in chamber 36 carries centrally thereof a pair of metal discs 41 and 42 clamped to the diaphragm by means fasteners such as indicated at 42' to provide a substantially rigid central region of the diaphragm assembly. The disc 41 is provided with a face 41a which is maintained substantially planar by the rigidity of the parts 41, 42, 42' throughout its range of movement and which defines a pressure control orifice 44 with a working fiuid discharge nozzle 46. Movement of the diaphragm assembly including parts 40, 41, 42 and 42' in response to changes in pressure in the chamber 36 is constrained so as to maintain the planar face 41a oriented substantially at right angles to the axis of nozzle 46 throughout the maximum operating range of movement. Movement of the diaphragm assembly toward nozzle 46 constricts the pressure control orifice 44 and raise the pressure in the working fluid passage 50 of the nozzle 46. A working pressure line 52 is shown for supplying working fluid to the passage 50 while an outlet line is indicated at 54 downstream of the pressure control orifice 44.

By way of example, the pilot fluid discharge nozzles 22 and 23 may be spaced apart by a distance of about 1 inch to define a neutral zone of positions of the'edge of the web which may then be varied between 0 and 1 inch by pivotal movement of the sensing head 10 about the axis of mounting pin 11. With the sensing head disposed at right anglesto the edge of the web as illustrated in FIGS. 1 and 2, the neutral range of positions may extend over a distance of l inch. By pivoting the sensing head in the counterclockwise direction as viewed in FIG. 1, the neutral range of positions of the edge of the web may be progressively reduced to increase the sensitivity of the system to changes in web position. Pivoting the sensing head in the clockwise position about the axis of pin 11 from the position shown in FIG. 1 will progressively increase the effective extent of the neutral zone.

Referring to FIG. 1, working fluid discharge nozzle is supplied with fluid under pressure via a supply line 61, and the diaphragm assembly associated with pressure chamber 35. controls an orifice leading to an exhaust line indicated at 62. The working fluid passages leading to the diaphragm controlled orifices such as 44, FIG. 2, are indicated diagrammatically by. lines 52 and 61 in FIG. 3 to facilitate correlation of FIGS. 1 and 3. Similarly the pilot jet supply line 19 has been indicated in FIG. 3. I

Setscrews are indicated at 64 and 65 in FIGS. 1 and 2 for retaining the working fluid discharge nozzles 46 and 60 at desired adjustable positions relative to the diaphragm assemblies such as 40,41, 42, 42. I

Referring to FIG. 3, reference numeral designates an air pressure supply line while reference numeral 72 designates a water pressure supply line. A flow control orifice is indicated at 74 for maintaining a substantially constant rate of flow of liquid to the pilot discharge nozzles. In the air pressure supply line are pressure regulators 76 and 78. The pressure in the line 80 between regulators 76 and 78 is tapped by means of a line 81 leading to a control chamber 100 of an actuator device 82 for an edge position correction device 84. Downstream of the regulator 78, line 85 leads to the working fluid supply lines 52 and 61 via respective flow control orifices 86 and 86'. The back pressure upstream of the respective pressure control ori fices such as 44 is supplied via lines 87 and 88 to respective control chambers 90 and 94 in actuator 82.

Referring to FIG. 4, the actuator is shown in an operating condition with an error being registered by the sensing head. indicating that the edge of the web is too far to the left as viewed in FIG. 1 so as to fail to obstruct the pilot fluid jet 23 which is associated with pressure chamber 36. In this event. there is a strong back pressure in each of the working fluid recting movement of the roll passages 52 and 61 which lead to the lines-88 and 87 (FIG. 3), respectively. Specifically there will be a high pressure in the chamber 90 depressing piston 91 against the action of compression spring 92, and there will also be a relatively high pressure in chamber 94 depressing piston 95 against the action of compression spring 96. The fluid pressure of line 87 is communicated with chamber 90 in all operating positions of the actuator, and line 88 is in communication with chamber 94 under operating conditions. Further, line 81 leading from the pilot jet line 80 is in communication with chamber 100 so as to raise piston 101 against the action of compression spring 102. The relatively high pressure in working pressure line 52 indicates an error and causes the edge correction mechanism 84 to assume the active condition indicated in FIG. 4. Specifically the error indicating high pressure in line 88 causes piston rod 104 to rock bell crank 105 about its pivot 106 so as to shift the connecting shaft 108 to the right as viewed in FIG. 4. This places a drive pawl 110 in driving relation to the rachet wheel 111 so that the rotation of the correction roll 115 causes successive increments of rotation of the rachet wheel lll and the associated parts. Specifically a disc 120 rotates with the correction roll shaft 121 so as to drive the connecting link 124 with an oscillatory and up and down motion. This motion is guided by means of a link 126 having a fixed pivot point 127 and a movable pivot connection at 128 with the rod 124. The result is that when an error is present, each revolution of the correction roll 115 on its axis causes an increment of rotation of the rachet wheel 111, shifting the roll end support 129 and actuator 84 by means of the nut 130 secured with the rachet wheel 111 and threadedly engaging the stationary threaded shaft 132 mounted in the roller frame 134. The progressive movement of the nut 130 along the threaded shaft 132 causes progressive angular adjustment of the roll end support 129 to provide a progressively increasing error correction as long as the error of the given polarity is present. The operation is entirely comparable when the edge of the web obstructs both of the pilot discharge nozzles 22 and 23 giving rise to relatively low pressures at lines 87 and 88. Specifically, the bell crank 105 moves to an opposite extreme (in the counterclockwise direction as viewed FIG. 4) to initiate progressive edge cor- 115 in the opposite direction. The rachet device for producing the progressive edge correcting angular adjustment of the roll 115 is itself conventional and need not be further described.

FIG. 3 shows the edge position correction device 84 in a quiescent condition as a result of a failure of either air pressure at line 70 or water pressure at line 72. In the case of a failure of air pressure at line 70, it will be observed that there will be a drop in pressure at line 81, reducing the pressure in chamber 100 and allowing piston 101 to be urged to the limit ofits travel by means of the compression spring 102. In this condition of actuator 82, the edge correction roll 115 is maintained in its current angular position and no further edge correcting angular adjustments thereof are possible even though the air pressure signals at lines 87 and 88 indicate a continuing error in the position of the web. Thus in the event of an air supply failure the actuator 82 assumes the fail-safe" condition indicated in FIG. 3 to hold the guide roller 115 at its current position.

In the event of a'failure of water pressure at line 72, a diaphragm operated valve 140 receives its chamber communicating with the line 72 so as to operate a valve indicated at 141 which then blocks incoming line 70 and dumps air pressure from line 143 via a discharge line 142. The pressure regulators 76 and 78 are capable of back dumping any air pressure in lines 80, 81 and 85 upon the occurrence of a supply pressure failure so as to quickly relieve the pressure in chamber 100. Thus line 81 experiences a reduction in air pressure both in the case of a water supply failure and in the case of an air supply failure, and the pressure in line 81 may also be utilized to control operation of a warning light or bell, or shutting off any part or all of the operation.

a reduced pressure in By way of example and not of limitation, the following specific parameters are employed in a preferred embodiment in accordance with the present invention. The cylinders providing chambers 100, and 94 are substantially of 1 inch diameter with respective pistons 101, 91 and serving to seal the respective chambers and prevent substantial leakage therefrom to the spring side of the respective pistons. The lines 81, 87 and 88 of course communicate with the respective chambers at positions such that communication with the chambers is maintained in all operation positions of the respective pistons. The pistons have substantially a Vs-inch stroke. In each control chamber section -of actuator 82, but particularly in the upper failsafe section, a spring return diaphragm actuator may be used instead of a piston actuator to avoid friction or corrosion binding.

The fail-safe actuator section maynot be called upon for months at a time and thus presents a particularly critical problem in the achievement of reliable operation.

For the case of sensing the position of felt webs in'paper machines, air pressure would be supplied to line 72 rather than water pressure.

In the illustrated embodiment, the sensing head preferably has a web receiving gap between the discharge orifices .of nozzles 22 and 23 and the exterior surface 32 of about 1% inch for sensing the position of paper machine felts and wires. The neutral zone which is adjusted by twisting the sensing head 10 preferably may be adjusted over a range of from about 0 to about 1 inch. The operating pressure at the pilot jets can be as low as about 2 inches of water column and as high as about l0 pounds per square inch above atmospheric pressure; thefonly limitation at 10 pounds per square inch would be that overloading of the internal diaphragms such as 40 should be avoided. The pilot pressure is determined by how much back pressure is desired in the lines 87 and 88 and preferably is sufficient so that the output pressure variation from the,head at lines 87 and 88 is sufficient to directly control operation of .the edge position correcting device 84. For a wire or felt on a paper making machine a typical setting of pilot pressure is about 5 pounds per square inch above atmospheric pressure so as to provide an entirely ample air pressure on the pilot jets without overtaxing the diaphragm material 38. The kinetic energy of the pilot jets from nozzles 22 and 23 is converted .to static pressure within the diaphragm chambers 35 and 36, and it is estimated that there is at least approximately 75 percent recovering of the kinetic energy in the form of static pressure within the diaphragm chambers. Where the working fluid discharge nozzles 46 and 60 are concerned, the diameter of the working fluid passages such as 50 should be about oneeighth inch, and the diaphragm assemblies such as 40, 41, 42, 42 should have an effective diameter exposed to pressure in the chambers such as 36 of about 1 inch to provide respective areas of 0.003 square inch and 0.7854 square inch, or an amplification factor of about 261 to l.

The diaphragm 38 is preferably made of a nylon fabric which is impregnated with neoprene. The thickness .of the material is approximately 0.030 inch. The diaphragm lhas a metal disc 41 glued on at the center, and secured by rivets such as 42' as shown in FIG. 2, metal disc 41 being approximately three-eighths inch in diameter and having atravcl of approximately one-sixteenth inch between a position blocking the working air stream from passage 50 and a position essen tially completely venting the working air stream topassage 54.

The overall length of the sensing head for example along the lower member 18 as viewed in FIG. 2 is approximately 8 inches, while the vertical span of the sensing head, vertically as viewed in FIG. 2 has an overall dimension of about 4 inches, the parts being illustrated substantially to scale in FIGS. .1 and 2.

It may be noted that is also possible to operate the system by supplying air under pressure to the pilot discharge nozzles 22 and 23 and supplying water under pressure to the lines 52 and 61.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

We claim: 1. A fluid sensing and amplifying system comprising: a sensing head having a web receiving space, said head having a pilot fluid discharge nozzle at one side of said space and directed through said space for emitting a pilot fluid jet capable of being substantially intercepted by the edge of the web in one predetermined lateral position of the web while being substantially unobstructed by the edge of the web in another lateral position of the web;

said head having wall means with an exterior surface at the opposite side of the web receiving space from the pilot fluid discharge nozzle, and having an interior fluid pressure chamber, with a fluid passage extending from the exterior surface to said chamber and opening at said exterior surface in substantial alignment with said pilot fluid discharge nozzle to provide fluid communication to said chamber for the fluid of said pilot fluid jet, to the extent that the pilot fluid jet is not intercepted by the edge of the web, the pressure in said chamber varying in accordance with the degree of interception of the pilot fluid jet by the edge of the web;

diaphragm means having one side thereof defining a boundary of said chamber so as tobe responsive to the pressure within said chamber; and

a working fluid discharge nozzle directed toward the opposite side of said diaphragm means, said diaphragm means having an orifice defining surface cooperating with said working fluid discharge nozzle to define a pressure control orifice whose flow area varies in accordance with the position of said diaphragm means, the diaphragm means having a substantially greater effective area responsive to the pressure in said chamber than the flow area of said working fluid discharge nozzle for substantial amplification of the variations in pressure in said chamber as a function of the position of the edge of the web in relation to the pilot fluid jet.

2. A fluid sensing and amplifying system according to claim 1 with said diaphragm means having a plate with a planar face providing said orifice defining surface, said plate being constrained for shifting movement substantially axially of the working fluid discharge nozzle and in a direction substantially normal to said planar face in response to pressure variations in said chamber.

3. A fluid sensing and amplifying system according to claim 2 with said plate being constrained for movement substantially axially of the working fluid discharge nozzle over a range of movement of the order of one-sixteenth inch without deflection of said planar face from a substantially planar configuration and without shifting of the plate from a substantially perpendicular relationship to the axis of said working fluid discharge nozzle.

4. A fluid sensing and amplifying system according to claim 2 with said diaphragm means having substantial resiliency tending to maintain said planar face of said plate in a position relatively remote from said working fluid discharge nozzle when the edge of the web is in a position substantially obstructing said pilot fluid jet so as to provide a relatively low working pressure upstream of said pressure control orifice of said working fluid discharge nozzle and the velocity pressure of the pilot fl'uid jet in the absence of substantial obstruction by the edge of the web being converted into a pressure in said chamber sufficient to displace said planar face toward said working fluid discharge nozzle a distance of the order of onesixteenth inch to provide a substantially increased working pressure upstream of said pressure control orifice in said working fluid pressure discharge nozzle.

5. A fluid sensing and amplifying systemin accordance with claim 1 with said diaphragm means having an effective diameter of the order of 1 inch and the flow area of said working fluid discharge nozzle being of the order of' one-eighth inch.

6. A fluid sensing and amplifying system in accordance with claim 5 with said diaphragm means being of resilient material having a metal plate secured thereto at a central portion thereofand providing said orifice defining surface.

7. A fluid sensing and amplifying system in accordance with claim 1 with said pilot fluid discharge nozzle supplying a pilo fluid jet of water.

8. A fluid sensing and amplifying system in accordance with claim 7 with said working fluid discharge nozzle supplying a working fluid jet of air under pressure to said pressure control orifice for control by the water pressure variation in said chamber. I

9. A fluid sensing and amplifying system in accordance with claim 7 with said web receiving space having a dimension in the direction axially of the pilot fluid discharge nozzle of the order of 1 /2 inch.

10. A fluid sensing and amplifying system in accordance with claim 9 with the pressure upstream of the pilot fluid discharge nozzle being of the order of 5 pounds per square inch above atmospheric pressure.

11. A fluid sensing and amplifying system in accordance with claim 1 with a web position control device for driving the web in respective opposite lateral directions, said device being progressively movable in opposite web correcting directions in response to continuing web errors of respective opposite polarities and having successive quiescent conditions providing successive degrees of web position correction, a fluid pressure responsive actuator for selectively conditioning said device for progressive movements thereof and for quiescent operation thereof, said head having two pilot fluid discharge nozzles defining respective limit positions for the edge of thc web and having two working fluid discharge nozzles supplying respective working fluid jets and responsive to the obstruction of the respective pilot fluid jets to vary the working pressures upstream of respective pressure control orifices, and means providing fluid communication from upstream of the respective pressure control orifices to said actuator for causing progressive movement of the device in one direction when both pilot fluid jets are obstructed and for causing progressive movement of the device in the opposite direction when neither pilot fluid jet is obstructed and forshifting the device to the quiescent condition when the edge of the web is in a neutral zone neutral zone between the two pilot fluid jetsv 12. A fluid sensing and amplifying system in accordance with claim 11 with working pressure supply means for supplying working pressure upstream of said working fluid discharge nozzles, and means coupled to said working pressure supply means responsive to a failure of working pressure for operating said actuator to maintain said device in quiescent condition.

13. A fluid sensing and amplifying system in accordance with claim 12 with pilot pressure supply means for supplying fluid pressure upstream of said pilot fluid discharge nozzles, and means coupled with said pilot pressure supply means for sensing a failure of pilot pressure and responsive to a failure of pilot pressure to shift said device to quiescent condition.

14. A fluid sensing and amplifying system in accordance with claim 12 with said working pressure supply means supplying air under pressure upstream of the working fluid discharge nozzles and with pilot pressure supply means supplying water under pressure upstream of said pilot fluid discharge nozzles, and means coupled to said pilot pressure supply means and responsive to a failure in water pressure to dump air pressure from the working pressure supply means, whereby said actuator is operated to shift the device to quiescent condition in response to a failure in either working air pressure or pilot water pressure.

15. A fluid sensing and amplifying system comprising:-

a web position control device which is progressively movable in respective opposite direction from a neutral position in response to continuing errors in the position of a web;

when the edge of the web is outside of-said neutral range of positions in respective opposite lateral directions and for maintaining said actuator in the neutral condition when the edge of the web is in said neutral range of positions; and

means coupled with said sensing head and with said actuator and responsive to a failure of supply pressure to said head for maintaining said actuator in said neutral condition. 

1. A fluid sensing and amplifying system comprising: a sensing head having a web receiving space, said head having a pilot fluid discharge nozzle at one side of said space and directed through said space for emitting a pilot fluid jet capable of being substantially intercepted by the edge of the web in one predetermined lateral position of the web while being substantially unobstructed by the edge of the web in another lateral position of the web; said head having wall means with an exterior surface at the opposite side of the web receiving space from the pilot fluid discharge nozzle, and having an interior fluid pressure chamber, with a fluid passage extending from the exterior surface to said chamber and opening at said exterior surface in substantial alignment with said pilot fluid discharge nozzle to provide fluid communication to said chamber for the fluid of said pilot fluid jet, to the extent that the pilot fluid jet is not intercepted by the edge of the web, the pressure in said chamber varying in accordance with the degree of interception of the pilot fluid jet by the edge of the web; diaphragm means having one side thereof defining a boundary of said chamber so as to be responsive to the pressure within said chamber; and a working fluid discharge nozzle directed toward the opposite side of said diaphragm means, said diaphragm means having an orifice defining surface cooperating with said working fluid discharge nozzle to define a pressure control orifice whose flow area varies in accordance with the position of said diaphragm means, the diaphragm means having a substantially greater effective area responsive to the pressure in said chamber than the flow area of said working fluid discharge nozzle for substantial amplification Of the variations in pressure in said chamber as a function of the position of the edge of the web in relation to the pilot fluid jet.
 2. A fluid sensing and amplifying system according to claim 1 with said diaphragm means having a plate with a planar face providing said orifice defining surface, said plate being constrained for shifting movement substantially axially of the working fluid discharge nozzle and in a direction substantially normal to said planar face in response to pressure variations in said chamber.
 3. A fluid sensing and amplifying system according to claim 2 with said plate being constrained for movement substantially axially of the working fluid discharge nozzle over a range of movement of the order of one-sixteenth inch without deflection of said planar face from a substantially planar configuration and without shifting of the plate from a substantially perpendicular relationship to the axis of said working fluid discharge nozzle.
 4. A fluid sensing and amplifying system according to claim 2 with said diaphragm means having substantial resiliency tending to maintain said planar face of said plate in a position relatively remote from said working fluid discharge nozzle when the edge of the web is in a position substantially obstructing said pilot fluid jet so as to provide a relatively low working pressure upstream of said pressure control orifice of said working fluid discharge nozzle and the velocity pressure of the pilot fluid jet in the absence of substantial obstruction by the edge of the web being converted into a pressure in said chamber sufficient to displace said planar face toward said working fluid discharge nozzle a distance of the order of one-sixteenth inch to provide a substantially increased working pressure upstream of said pressure control orifice in said working fluid pressure discharge nozzle.
 5. A fluid sensing and amplifying system in accordance with claim 1 with said diaphragm means having an effective diameter of the order of 1 inch and the flow area of said working fluid discharge nozzle being of the order of one-eighth inch.
 6. A fluid sensing and amplifying system in accordance with claim 5 with said diaphragm means being of resilient material having a metal plate secured thereto at a central portion thereof and providing said orifice defining surface.
 7. A fluid sensing and amplifying system in accordance with claim 1 with said pilot fluid discharge nozzle supplying a pilot fluid jet of water.
 8. A fluid sensing and amplifying system in accordance with claim 7 with said working fluid discharge nozzle supplying a working fluid jet of air under pressure to said pressure control orifice for control by the water pressure variation in said chamber.
 9. A fluid sensing and amplifying system in accordance with claim 7 with said web receiving space having a dimension in the direction axially of the pilot fluid discharge nozzle of the order of 1 1/2 inch.
 10. A fluid sensing and amplifying system in accordance with claim 9 with the pressure upstream of the pilot fluid discharge nozzle being of the order of 5 pounds per square inch above atmospheric pressure.
 11. A fluid sensing and amplifying system in accordance with claim 1 with a web position control device for driving the web in respective opposite lateral directions, said device being progressively movable in opposite web correcting directions in response to continuing web errors of respective opposite polarities and having successive quiescent conditions providing successive degrees of web position correction, a fluid pressure responsive actuator for selectively conditioning said device for progressive movements thereof and for quiescent operation thereof, said head having two pilot fluid discharge nozzles defining respective limit positions for the edge of the web and having two working fluid discharge nozzles supplying respective working fluid jets and responsive to the obstruction of the respective pilot fluid jets to vary the working pRessures upstream of respective pressure control orifices, and means providing fluid communication from upstream of the respective pressure control orifices to said actuator for causing progressive movement of the device in one direction when both pilot fluid jets are obstructed and for causing progressive movement of the device in the opposite direction when neither pilot fluid jet is obstructed and for shifting the device to the quiescent condition when the edge of the web is in a neutral zone neutral zone between the two pilot fluid jets.
 12. A fluid sensing and amplifying system in accordance with claim 11 with working pressure supply means for supplying working pressure upstream of said working fluid discharge nozzles, and means coupled to said working pressure supply means responsive to a failure of working pressure for operating said actuator to maintain said device in quiescent condition.
 13. A fluid sensing and amplifying system in accordance with claim 12 with pilot pressure supply means for supplying fluid pressure upstream of said pilot fluid discharge nozzles, and means coupled with said pilot pressure supply means for sensing a failure of pilot pressure and responsive to a failure of pilot pressure to shift said device to quiescent condition.
 14. A fluid sensing and amplifying system in accordance with claim 12 with said working pressure supply means supplying air under pressure upstream of the working fluid discharge nozzles and with pilot pressure supply means supplying water under pressure upstream of said pilot fluid discharge nozzles, and means coupled to said pilot pressure supply means and responsive to a failure in water pressure to dump air pressure from the working pressure supply means, whereby said actuator is operated to shift the device to quiescent condition in response to a failure in either working air pressure or pilot water pressure.
 15. A fluid sensing and amplifying system comprising: a web position control device which is progressively movable in respective opposite direction from a neutral position in response to continuing errors in the position of a web; a fluid pressure operated actuator having a first condition for producing progressive movement of the device in one direction, having a second condition for producing progressive movement of the device in the opposite direction and having a third neutral condition for maintaining the device quiescent; a sensing head for sensing the position of the edge of a web associated with said web position control device and coupled with said actuator, said head having a neutral range of web positions and being operative for shifting said actuator respectively to the first and second conditions when the edge of the web is outside of said neutral range of positions in respective opposite lateral directions and for maintaining said actuator in the neutral condition when the edge of the web is in said neutral range of positions; and means coupled with said sensing head and with said actuator and responsive to a failure of supply pressure to said head for maintaining said actuator in said neutral condition. 